x86: add cache-as-ram migration option

There are some boards that do a significant amount of
work after cache-as-ram is torn down but before ramstage
is loaded. For example, using vboot to verify the ramstage
is one such operation. However, there are pieces of code
that are executed that reference global variables that
are linked in the cache-as-ram region. If those variables
are referenced after cache-as-ram is torn down then the
values observed will most likely be incorrect.

Therefore provide a Kconfig option to select cache-as-ram
migration to memory using cbmem. This option is named
CAR_MIGRATION. When enabled, the address of cache-as-ram
variables may be obtained dynamically. Additionally,
when cache-as-ram migration occurs the cache-as-ram
data region for global variables is copied into cbmem.
There are also automatic callbacks for other modules
to perform their own migration, if necessary.

Change-Id: I2e77219647c2bd2b1aa845b262be3b2543f1fcb7
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/3232
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

1 files changed, 12 insertions, 0 deletions

diff --git a/src/arch/x86/init/romstage.ld b/src/arch/x86/init/romstage.ld
index 88c56573ae..f44185f24e 100644
--- a/src/arch/x86/init/romstage.ld
+++ b/src/arch/x86/init/romstage.ld
@@ -35,6 +35,10 @@ SECTIONS
 		*(.rodata.*);
 		*(.rom.data.*);
 		. = ALIGN(16);
+		_car_migrate_start = .;
+		*(.car.migrate);
+		_car_migrate_end = .;
+		. = ALIGN(16);
 		_erom = .;
 	}
 
@@ -48,8 +52,16 @@ SECTIONS
 
 	. = CONFIG_DCACHE_RAM_BASE;
 	.car.data . (NOLOAD) : {
+		_car_data_start = .;
 		*(.car.global_data);
+		/* The cbmem_console section comes last to take advantage of
+		 * a zero-sized array to hold the memconsole contents that
+		 * grows to a bound of CONFIG_CONSOLE_CAR_BUFFER_SIZE. However,
+		 * collisions within the cache-as-ram region cannot be
+		 * statically checked because the cache-as-ram region usage is
+		 * cpu/chipset dependent. */
 		*(.car.cbmem_console);
+		_car_data_end = .;
 	}
 
 	_bogus = ASSERT((SIZEOF(.car.data) <= CONFIG_DCACHE_RAM_SIZE), "Cache as RAM area is too full");